The catalytic system titanocene difluoride/diphenylsilane used in the
catalytic hydrodefluorination (HDF) of aromatic, olefinic and allylic
fluoroorganic compounds was investigated focusing on the aspects regeneration
of the catalytically active species, substrate scope and regioselectivity. The
catalyst regeneration, the reaction of titanocene (III) fluoride with diphenyl
silane is an endergonic process. Depending on the barrier height of the HDF
reaction, regeneration becomes the rate-determine step; which has shown by
experimental and theoretical studies. Cp*2TiBH4 was synthesized for the first
time and analyzed by 11B- and 1H-NMR spectroscopy and by single crystal x-ray
diffraction, in the course of experimental investigations of the HDF
mechanism. Several functionalized and non-functionalized perfluoroarenes were
tested as substrates. Those having donor functional groups react only
stoichiometrically because they form stable LEWIS acid/base adducts with
titanocene (III) fluoride. Intramolecular regioselectivity was investigated
using perfluoroallylbenzene. 1st HDF takes place at the C3F5-moiety and 2nd
HDF at the aromatic moiety. For 1st HDF a mixture of allyic and vinylic
products was obtained. The HDF mechanism for fluoroarenes and
hexafluoropropene was investigated by combined experimental and theoretical
studies. Depending on orientation of the reactands F/H-exchange proceeds via
different energetically similar mechanisms. Attack of the nucleophilic hydride
mirrors the key step for aromatic and olefinic HDF. Because of the similarity
and redox stability of Cp2ScH and Cp2ScF compared to the previously described
titanium(III) species, scandocene derivatives should be investigated regarding
their reactivity with fluoroorganic compounds. In preliminary studies 45Sc-
und 1H-NMR studies of scandiumtrichloride adducts in solution were conducted.
Three different synthetic strategies were followed for the synthesis of
scandocene derivatives. Literature data of known scandium complexes could be
completed by the 45Sc NMR data. A scandocene amido complex could be
synthesized the first time and analyzed by NMR spectroscopy.